KR100657297B1 - Method of radial tilt detection and optical recording and/or reproducing apparatus for realizing it - Google Patents

Abstract

Forming first and second side light spots having a coma aberration of opposite signs when the optical information storage medium is not tilted on both the central light spot and the central optical spot in the tangential direction on the optical information storage medium; Wow; Dividing the central light beam corresponding to the central light spot reflected from the optical information storage medium into three first to third light regions spatially; Detecting a first light spot corresponding to the first light region by dividing the first light spot into two radial directions, and detecting second and third light spots corresponding to the second and third light regions, respectively; A signal detected by dividing the first and second side light beams corresponding to the first and second side light spots reflected from the optical information storage medium in two directions, respectively, and dividing the first light spot in two directions, in the radial direction. Detecting the first center push-pull signal, the second center push-pull signal as a difference between the signals that detect the second and third light spots as a difference of the two; Detecting first and second side push-pull signals from the first and second side light spots formed on the optical information storage medium using the first and second side light beam detection signals; A radial tilt signal obtained by obtaining a correction signal as a difference between the first and second center push-pull signals and subtracting a correction signal multiplied by a predetermined coefficient from a sum signal of the first and second side push-pull signals. Disclosed is a radial tilt detection method comprising a; and an optical recording and / or reproducing apparatus capable of realizing the same.

Description

Radial tilt detection method and optical recording and / or reproducing apparatus capable of realizing the same {Method of radial tilt detection and optical recording and / or reproducing apparatus for realizing it}

1 shows an optical spot on an optical disk surface, an arrangement of defocused optical spots on a photodetector, and a signal processor according to a conventional tilt detection method disclosed in US Pat. No. 5,751,680.

2 schematically shows an embodiment of an optical recording and / or reproducing apparatus capable of realizing a radial tilt signal detection method according to an embodiment of the present invention, in which a radial tilt signal in which an objective lens shift is corrected can be detected. .

3 illustrates an embodiment of the second diffractive optical element of FIG. 2 and a light beam LB incident thereto.

4 illustrates an embodiment of an optical spot formed on the optical information storage medium of FIG. 2, a photodetector structure in which a defocused optical spot is received, and a signal processor.

Fig. 5 shows the effect of the objective shift on the radial tilt signal. Figs. 6 and 7 show opposite signs and a certain amount of coma aberration when there is no radial tilt and when there is a radial tilt of 1 °, respectively. And the layout when the first and second side light beams are formed as first and second side light spots on the optical information storage medium, and the exit holes of the first and second side light beams reflected from the optical information storage medium. Shows the intensity distribution at.

FIG. 8 illustrates a first side push-pull signal SPP1 from a first side light spot formed on an optical information storage medium and a second side push from a second side light spot when there is no radial tilt as shown in FIG. 6. The full signal SPP2 and the radial tilt signal RTS obtained by the detection method according to the present invention are shown.

FIG. 9 shows the first side push-pull signal SPP1 from the first side light spot formed on the optical information storage medium and the first side from the second side light spot when there is a radial tilt of 1 ° as shown in FIG. The two-side push pull signal SPP2, the radial tilt signal RTS obtained by the detection method according to the present invention is shown.

FIG. 10 shows a typical push-pull signal when a radial tilt of 1 ° occurs in the BD and the first and second side light spots used to obtain the radial tilt signal have comma aberrations of W ₃₁ = 1λ of opposite signs. (PP) and the radial tilt signal (RTS) detected according to the present invention are shown in comparison.

Fig. 11 shows the relationship between the radial tilt detection sensitivity and the coma amount of the side light spots when the radial tilt detection method according to the present invention is used.

12 shows a radial tilt signal according to the radial tilt angle when using the radial tilt detection method according to the present invention.

<Description of the symbols for the main parts of the drawings>

10 ... light source 11,130 ... first and second diffractive optical element

20 ... Optical storage medium 21 .... Objective lens

150 ... Photodetector 170 ... Signal Processing Unit

The present invention relates to a radial tilt detection method and an optical recording and / or reproducing apparatus capable of realizing the same.

A general trend in the field of information storage, particularly in the field of optical information storage, is to increase the recording density further. An objective lens having a high number of apertures is used for optical pickup to generate a small spot size on the disk-shaped optical information storage medium (ie, optical disk) surface.

The rotating optical disc is tilted in the radial direction with respect to the objective lens due to its shape defects and drive mechanics. Tilt of the optical disc causes aberrations, mainly coma aberrations, and undesirably causes changes in spot size, shape and position. As a result, recording / reproducing characteristics deteriorate. In order to maintain good high density recording / playback performance, accurate high frequency detection and correction of the disc radial tilt is required during recording / playback.

In the well-known conventional tilt detection method, a separate tilt sensor is used to form light spots on the disk surface, to detect the intensity of the reflected light beam, and to subtract signals corresponding to the reflected light intensity, thereby subtracting these signals. Is used as the radial tilt signal.

According to this conventional tilt detection method, since the auxiliary light spot for tilt detection is placed far from the main light spot used for recording / reproducing, it is impossible to guarantee the tilt detection with sufficient accuracy. As a result, it is impossible to obtain information on local tilt variations.

Another conventional tilt detection method is disclosed in US Pat. No. 5,751,680. 1 shows an arrangement of light spots LBm '(LBs1') (LBs2 ') on the surface of an optical disc 1 according to a conventional tilt detection method disclosed in the above-mentioned US patent, an arrangement of defocused light spots on the photodetector 3, and The signal processor 7 is shown.

Referring to FIG. 1, in the U.S. patent, three light spots LBm '(LBs1') LBs2 'are formed on the surface of the optical disc 1 using beams having the same numerical aperture. A central light spot LBm 'having a nearly or exactly symmetrical rounded shape lies on the track center. The first and second side light spots LBs1 'and LBs2' each having a predetermined amount of commas of opposite signs equally and whose axis of symmetry are approximately or exactly perpendicular to the track direction are center light spots. It lies on the track in parallel in the tangential direction symmetrically with respect to (LBm ').

The center photodetector 4 is used to detect the center push-pull signal CPP 'from the center light spot LBm' focused on the optical disk 1 surface, and use this signal as an input for track servo.

In the closed tracking servo loop state, signals corresponding to light intensities reflected from the first and second side light spots LBs1 'and LBs2' are detected. More specifically, the reflected light intensities corresponding to the first and second side light spots LBs1 'and LBs2' are not divided but have first and second side photodetectors 5 and 6 having an area. Is detected by. The difference signal is used as the radial tilt signal RTS 'by subtracting signals corresponding to the reflected light intensities of the first and second side light spots LBs1' and LBs2 '.

When the optical disc 1 is not tilted, the coma amount, shape and size of the side light spots LBs1 'and LBs2' are the same. The light intensity reflected from the first side light spot LBs1 'is the same as the light intensity reflected from the second side light spot LBs2'. Therefore, the signal corresponding to the light intensity difference is zero.

Optical disc radial tilt causes coma aberration. Thereby, the coma amount in the side light spot LBs1 '(LBs2') changes. The amount of coma in one of the two side light spots LBS1 'and LBs2' increases, while the amount of coma decreases in the other. As such, when the radial tilt occurs, the shape and size of the side light spots LBS1 'and LBS2' are different.

Thereby, the reflected light intensity originating from the first side light spot LBs1 'is not the same as the reflected light intensity originating from the second side light spot LBs2'. The non-zero signal corresponding to this light intensity difference is the tilt signal.

According to this conventional method, it is possible to realize high frequency tilt detection. Since all three light spots used are located in close proximity to each other (typically 20 to 40 μm), it is possible to realize local tilt detection in the vicinity of the center light spot.

However, such a conventional method is very limited in accuracy because of its low tilt detection sensitivity when applied to a recordable land / groove medium. This is the result of an extremely small difference between the reflected light intensity originating from the first side light spot LBs1 'and the reflected light intensity originating from the second side light spot LBs2'. Therefore, it is impossible to realize accurate tilt detection for a recordable land / groove optical disc by using this conventional method.

On the other hand, the objective lens used for the optical pickup to form a small sized light spot on the optical disk surface is moved by the actuator in the radial direction to perform tracking. Thus, the relative position of the objective lens relative to the photodetector is not fixed, whereby the light reflected from the optical information storage medium and formed as a defocused spot on the photodetector moves across the photodetector in response to the objective lens shift. .

As described above, when recording / reproducing the optical information storage medium, an objective lens shift may occur, and this objective lens shift may affect the radial tilt signal, as can be seen in FIG. 5 to be described later.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and has an enhanced tilt detection sensitivity capable of accurately detecting the tilt of a recordable land / groove information storage medium. The present invention provides a radial tilt detection method capable of accurately detecting a radial tilt signal even in an objective lens shift, and an optical recording and / or reproducing apparatus capable of realizing the same.

Radial tilt detection method according to the present invention for achieving the above object, when the optical information storage medium on the optical information storage medium and the optical information storage medium is not tilted on both sides of the central optical spot in the tangential direction Forming first and second side light spots having a coma aberration of? Divides a central light beam corresponding to the central light spot reflected from the optical information storage medium in three spatially, and divides the first light region corresponding to one light region in the tangential direction and the remaining light region in two radial directions. Spatially dividing into second and third light areas corresponding to the two light areas; Detecting the first optical spot corresponding to the first optical region by dividing the optical beam into two radial directions, and detecting the second and third optical spots corresponding to the second and third optical regions, respectively; Dividing and detecting the first and second side light beams corresponding to the first and second side light spots reflected from the medium in a radial direction, respectively; The first center push-pull signal is detected as the difference between the signals detected by dividing the first light spot in the radial direction, and the second center push-pull signal is detected as the difference between the signals that detect the second and third light spots. Making a step; Using the first and second side light beam detection signals, a first side push pull signal from a first side light spot formed on the optical information storage medium and a second side push pull signal from a second side light spot Detecting; A radial obtained by obtaining a correction signal as a difference between the first and second center push-pull signals and subtracting the correction signal multiplied by a predetermined coefficient from a sum signal of the first and second side push-pull signals; Detecting a tilt signal.

Here, it is preferable that the first and second side light spots have the same amount of coma aberration of opposite signs when the optical information storage medium is not tilted.

The first and second side light spots are preferably formed on the optical information storage medium such that the first and second side push pull signals detected therefrom have a phase difference of approximately 180 °.

The first and second side light spots are preferably formed on the optical information storage medium symmetrically with respect to the center light spot in the tangential direction.

An optical recording and / or reproducing apparatus according to the present invention for achieving the above object comprises: a light source; The light beam emitted from the light source is diffracted, divided into a central light beam and first and second side light beams, and a central light spot corresponding to the central light beam on the optical information storage medium, and optical information storage in both of the central light spots. A first diffractive optical element for forming first and second side light spots corresponding to the first and second side light beams having comma aberrations opposite to each other when the medium is not tilted; The objective lens focuses the incident light onto the optical information storage medium, and spatially splits the central light beam corresponding to the central optical spot reflected from the optical information storage medium to correspond to one optical region in the tangential direction. A second diffractive optical element for spatially dividing the first optical region into second and third optical regions corresponding to two optical regions in which the remaining optical region is divided into two in the radial direction; Defocused first to third light spots corresponding to the first to third light regions are formed, the first light spot is divided into two in the radial direction, and the second and third light spots are respectively detected. And a photodetector including a central photodetector configured to detect the first and second side light beams reflected from the optical information storage medium in two radial directions, respectively. A first side push-pull signal from a first side light spot formed on the optical information storage medium and a second side light spot using a pickup and detection signals of the first and second side photodetectors; The first center push-pull signal, the second and the third are detected as the difference between the two side push-pull signals and the signals detected by splitting the first light spot in the radial direction using the detection signals of the center photodetector. Detect light spot Detect a second center push-pull signal as a difference of signals, detect a correction signal as a difference between a first and second center push-pull signal, apply a predetermined coefficient to the correction signal, and apply the first and second side push-pull And a signal processor configured to detect the radial tilt signal in which the objective lens shift is corrected by subtracting a correction signal to which a predetermined coefficient is added from the sum of the signals.

Here, the second diffractive optical element includes a quarter wave plate having a polarization diffraction element for diffracting light selectively according to the polarization of the incident light, and changing the polarization of the incident light between the second diffraction optical element and the objective lens; It may further include.

The first diffractive region may be formed to correspond to a semicircle of the light beam, and the second and third diffractive regions may be formed to correspond to a quadrant of the light beam.

Hereinafter, a radial tilt detection method and an optical recording and / or reproducing apparatus capable of realizing the same will be described in detail with reference to the accompanying drawings.

FIG. 2 schematically illustrates an embodiment of an optical recording and / or reproducing apparatus capable of realizing a tracking error signal detection method according to an exemplary embodiment of the present invention in which a radial tilt signal in which an objective lens shift is corrected can be detected. Shows. FIG. 3 shows an embodiment of the second diffractive optical element of FIG. 2 and a light beam LB incident thereto, and FIG. 4 shows an optical spot and defocus formed on the optical information storage medium 20 of FIG. An example of the structure of the photodetector 150 and the signal processor 170 in which the received light spot is received is shown.

2 to 4, the optical recording and / or reproducing apparatus according to an embodiment of the present invention forms light spots on the optical information storage medium 20 and receives and detects light beams reflected therefrom. And a signal processor 170 configured to detect the radial tilt signal using the pickup and the detection signal of the optical pickup.

The optical pickup uses the first diffractive optical element 11, for example, hologram grating, to divide the light beam emitted from the light source 10 into three light beams, that is, the main light beam, the first side light beam, and the second side light beam. The main light spot LBm, the first side light spot LBs1, and the second side light spot LBs2 are formed on the optical information storage medium 20, and the first and second sides are basically formed when there is no tilt. The light spots LBs1 and LBs2 have the same predetermined amount of coma aberration of opposite signs, and are irradiated on the track in a tangential direction parallel to the main light spot LBm, and are stored in an optical information storage medium. It has an optical configuration in which the light beam reflected from 20 can be divided into three parts and detected.

The optical pickup includes a light source 10, a first diffractive optical element 11 for dividing the light beam emitted from the light source 10 into the main light beam, the first and second side light beams, and the incident light to focus the light. An objective lens 21 for focusing on the information storage medium 20, a second diffractive optical element 130 for light splitting for detection of a correction signal for correcting the objective lens shift, and an optical information storage medium And a photodetector 150 for receiving the main light spot LBm, the first side light spot LBs1, and the second side light spot LBs2 that are received after being reflected at 20. In addition, the optical pickup may include an optical path converter 15 for converting an advancing path of incident light and a collimating lens 13 to inject parallel light into the objective lens 21.

The light source 10 emits light of a predetermined wavelength suitable for recording and / or reproducing the optical information storage medium 20. The light source 10 may be provided to emit light having a blue wavelength, for example, a wavelength of 405 nm. In this case, the optical recording and / or reproducing apparatus according to the present invention can record and / or reproduce an optical information storage medium using a blue wavelength of light, for example, BD or Advanced Optical Disc (AOD).

1 shows an example in which the optical pickup is a separate optical system in which the light source 10 and the photodetector 150 are separated, and each includes a light source 10 and a photodetector 150. The light source 10 may be provided to emit light having a single wavelength, for example, light having a blue wavelength having a wavelength of about 405 nm. In addition, the light source 10 may be a multi-type light source that emits light having a plurality of wavelengths so that a plurality of formats of optical information storage media such as BD (or AOD) and DVD can be used. The optical pickup may further include a hologram optical module (not shown) so as to be compatible with a plurality of formats of optical information storage media using light having different wavelengths. In addition, the optical configuration of the optical pickup may be variously modified.

The first diffractive optical element 11 diffracts a light beam incident from the light source 10 into a 0th order beam, a + 1st order beam, and a -1st order beam, and the 0th order light beam does not have coma aberration. The + 1st light beam and the -1th light beam are formed to have the same amount of coma aberration of opposite signs. By this diffraction, the light beam is separated into three light beams. At this time, the zeroth order light beam is the center light beam, the + 1st order light beam is, for example, the first side light beam, and the -first order light beam is, for example, the second side light beam.

The first diffractive optical element 11 may include holographic grating. In FIG. 4, the first and second side light beams LBs1 and LBs2 formed by focusing the first and second side light beams on the optical information storage medium 20 are opposite to each other in a direction perpendicular to the tangential direction. Show an example of having a coma aberration. In this case, when the optical information storage medium 20 is not tilted, coma aberration amounts, shapes, and sizes of the first and second side light spots LBS1 and LBS2 are the same, and only the signs thereof are reversed.

Here, the diffraction pattern of the first diffractive optical element 11 may vary depending on the direction in which coma aberration is formed, the amount, shape, and the like of the coma aberration. Examples of diffraction patterns of diffractive optical elements having such various coma aberration characteristics are disclosed in US Pat. No. 5,751,680.

The central light beam and the first and second side light beams separated by the first diffractive optical element 11 and passing through the objective lens 21 have the same numerical aperture and are focused on the optical information storage medium 20. It is formed on the track in the central light spot LBm, the first and second side light spots LBs1 and LBs2 in parallel in the tangential direction.

The central light spot LBm has a round shape that is almost or exactly symmetrical and is formed in the center of the groove (or land) of the optical information storage medium 20. The first and second side light spots LBs1 and LBs2 have the same predetermined amount of coma aberrations opposite to each other, and have a center light spot on the same groove (or land) in which the center light spot LBm is formed. And opposite each other in the tangential direction symmetrically with respect to LBm. The first and second side light spots LBs1 and LBs2 are grooves (or lands) such that the first and second side push-pull signals SPP1 and SPP2 described below have a phase difference of approximately or exactly 180 degrees. )

The second diffractive optical element 130 is preferably attached to a lens holder on which an objective lens 21 of an actuator (not shown) is mounted. The objective lens 21 is driven in the focus, tracking and / or tilt direction by the actuator while being mounted on the lens holder of the actuator.

Referring to FIG. 3, the second diffractive optical element 130 passes through the light incident from the light source 10 without dividing it, and the light reflected from the optical information storage medium 20 is incident to a T ″ shape. The first and second optical regions LB ₁ corresponding to one optical region in a tangential direction by dividing the structure into three parts, and two and third optical regions corresponding to two optical regions divided into two in the radial direction. LB ₂ ) LB _3. The central optical beam, the first and second side light beams reflected by the optical information storage medium 20 by the second diffractive optical element 130 are respectively the first through the second through the optical diffraction element 130. As shown in FIG. 4, spatially divided into a third light region LB ₁ (LB ₂ ) and an LB ₃ , the center photodetector 160, the first and second side photodetectors of the photodetector 150. 3, only one light beam LB incident on the second diffractive optical element 130 is illustrated in FIG. 3. The central light beam and the first and second side light beams branched by the first diffractive optical element 11 are incident on the element 130. In this case, the centers of the first and second side light beams are mutually opposite to the center light beam. It is positioned slightly shifted symmetrically, and this center shift is neglected because it is smaller than the assembling error of the objective lens 21 on the order of several μm. Therefore, only one light beam LB is shown in FIG.

The second diffractive optical element 130 preferably includes a polarization diffraction element, that is, a polarization hologram element that diffracts light selectively according to the polarization of incident light. In this case, the optical pickup according to the present invention further includes a quarter-wave plate 140 for changing the polarization of incident light on the optical path between the second diffractive optical element 130 and the objective lens 21. In this case, the quarter-wave plate 140 is preferably attached to the lens holder of the actuator together with the second diffractive optical element 130.

As the polarization diffraction element is well known, light of a specific polarization may be diffracted according to polarization of incident light, and light of another polarization orthogonal thereto may be transmitted straight. Therefore, it is possible to selectively diffract light in accordance with the polarization of the incident light.

The semiconductor laser used as the light source 10 emits laser light in which one linear polarization component is dominant. Therefore, in the semiconductor laser, approximately S-polarized or P-polarized light is emitted.

Accordingly, when the polarization diffraction element is configured to pass light of a predetermined linearly polarized light emitted from the light source 10 into the second diffraction optical element 130, the second diffraction optical element 130 passes straight through. One light becomes one circularly polarized light while passing through the quarter wave plate 140, and the one circularly polarized light is reflected by the optical information storage medium 20 and becomes light of another circularly polarized light. The circularly polarized light becomes light of another linearly polarized light which is orthogonal while passing through the quarter wave plate 140 again, and is diffracted by the second diffractive optical element 130.

As shown in FIG. 3, the second diffractive optical element 130 converts the light beam reflected from the optical information storage medium 20 into the first to third optical regions LB ₁ and LB ₂ and LB ₃ . The first to third diffraction areas 131, 133, and 135 are provided for dividing.

The first to third diffractive regions 131, 133, and 135 of the second diffractive optical element 130 are formed to divide the light beam reflected from the optical information storage medium 20 into a T-shaped structure. . The first diffraction region 131 may be formed to correspond to a 180 ° sector of the light beam LB, that is, a semicircle, and the diffraction pattern may be formed along the track direction, that is, the radial direction. The second and third diffractive regions 133 and 135 are formed so as to correspond to the 90 ° sector, that is, the quadrant of the light beam, and are formed along the 45 ° direction with respect to the track direction so that the diffraction pattern is 90 ° with respect to each other. Can be.

The second diffractive optical element 130 having such a configuration corresponds to the first to third diffractive regions 131, 133, and 135 of the cross section of the light beam LB reflected from the optical information storage medium 20. The first to third light regions LB ₁ (LB ₂ ) and LB ₃ are spatially divided.

Therefore, the central light beam and the first and second side light beams traveling toward the optical information storage medium 20 are irradiated onto the optical information storage medium 20 by passing through the second diffractive optical element 30 as it is without splitting the optical region. In addition, each of the central light beams reflected from the optical information storage medium 20 and each of the first and second side light beams passes through the second diffractive optical element 130 and includes the first to third optical regions LB ₁ and LB ₂ ( LB ₃ ) is spatially divided. In this case, the spatial division of the first to third optical regions LB ₁ , LB ₂ , and LB ₃ causes the light beam to be the first to third diffractive regions 131 and 133 of the second diffractive optical element 130. It is obtained by diffraction in the +1 or -1 order by (135).

On the other hand, when the second diffractive optical element 130 is provided with a polarization diffraction element, and provided with a quarter wave plate 140 between the second diffractive optical element 130 and the objective lens 21, the light source When light of approximately one linearly polarized light (S polarized light or P polarized light) is emitted from 10, it is reflected by the optical information storage medium 20 and is incident on the optical path converter 15 via the second diffractive optical element 130. The resulting light becomes light of another linearly polarized light orthogonal thereto.

Accordingly, the amount of light from the light source 10 to the optical information storage medium 20 and the light reflected from the optical information storage medium 20 and split by the second diffractive optical element 130 to the photodetector 150 is determined. In order to maximize, the optical path converter 15 is preferably provided with a polarizing beam splitter for selectively transmitting or reflecting the incident light according to the polarization.

As described above, the light beams reflected from the optical information storage medium 20 are spatially divided by the second diffractive optical element 130 and received by the photodetector 150.

As shown in FIG. 4, the photodetector 150 includes a central photodetector 160 in which a main light beam is defocused to form a main light spot, and first and second side light beams are defocused. First and second side photodetectors 153 and 155 formed as side light spots.

The central light beam spatially divided by the second diffractive optical element 130 and the first to third light regions LB ₁ (LB ₂ ) LB _{3 of} each of the first and second side light beams are shown in FIG. 4. As shown, the first to third light spots LB ₁ (LB ₂ ) defocused on the center photodetector 160, the first and second side photodetectors 51 and 153 of the photodetector 150. ) LB ₃ . The defocused first to third light spots LB ₁ (LB ₂ ) LB ₃ are spatially separated from each other.

4 shows an example in which the central photodetector 160 of the photodetector 150 is formed in a quadrant structure. As shown in FIG. 4, the center photodetector 160 splits and receives the defocused first light spot LB ₁ corresponding to the first light region LB ₁ of the center light beam in a radial direction. Defocused second and third light spots LB ₂ corresponding to the first and second light receiving areas 161 and 163, and the second and third light areas LB ₂ and LB ₃ of the central light beam. Third and fourth light receiving regions 165 and 167 for receiving LB ₃ , respectively. The first side photodetector 153 may include two light receiving regions 153a and 153b for dividing the first side photospot into two radial directions. The second side photodetector 155 may include two light receiving regions 155a and 155b for dividing the second side light spot in two directions in the radial direction.

The signal processor 170 may include first and second side push-pull signals SPP1 and SPP2 from the first and second sub light spots LBs1 and LBs2 focused on the optical information storage medium 20. ) And a correction signal (CS) from the detection signals of the first to fourth light receiving regions 161, 163, 165 and 167 of the center photodetector 160. signal) may be included.

Referring to FIG. 4, the signal processor 170 may generate first and second side push-pull signals SPP1 and SPP2 and obtain first and second differential synchronizers 172 and 174. And the adder 176, the third to fifth differential motors 171, 173 and 175, the gain adjuster 178, and the sum signal SPP1 + SPP2 for detecting the correction signal CS. And a sixth differential motor 177 which receives the signal k × CS multiplied by the correction coefficient k and the differential signal, and outputs the radial tilt signal RTS with the objective lens shift corrected. do.

The first differential actuator 172 uses the first side light spot LBs1 ′ defocused on the light receiving regions 153a and 153b of the first side photodetector 153, thereby providing an optical information storage medium 20. Generate a first side push-pull signal SPP1 from the first side light spot LBs1 focused on. The first side push-pull signal SPP1 is a difference signal of detection signals of the light receiving regions 153a and 153b obtained by dividing and receiving the defocused first side light spot LBs1 'by two.

 The second differential actuator 174 uses the defocused second side light spot LBs2 ′ formed in the light receiving regions 155a and 155b of the second side photodetector 155 to store the optical information storage medium 20. Generates a second side push-pull signal SPP2 from the second side light spot LBs2 focused on the &lt; RTI ID = 0.0 &gt; The second side push-pull signal SPP2 is a difference between detection signals of the light receiving regions 155a and 155b obtained by dividing and receiving the defocused second side light spot LBs2 '.

Here, the spatially divided first to third light regions LB ₁ (LB ₂ ) and LB _{3 of} each of the first and second side light beams are also disposed on the first and second side photodetectors 153 and 155. Although it is formed of the first to third light spots LB ₁ (LB ₂ ) (LB ₃ ) defocused, the first and second side photodetectors 153 and 155 are respectively divided into two radial directions. Since the regions 153a / 53b and 155a / 55b are used, even if the first and second side light beams are spatially divided into three, the detection signals of the first and second side photodetectors 153 and 155 are used. The first and second side push-pull signals SPP1 and SPP2 obtained by the same method have substantially the same characteristics as the case where the first and second side light beams are not spatially divided into three. Signal SPP1 SPP2 can be detected under a closed tracking servo loop.

The adder 176 sums the first and second side push-pull signals SPP1 and SPP2 and outputs the sum signals SPP1 and SPP2.

When there is no radial tilt, the first side push-pull signal from the first side light spot LBs1 since the amount of coma aberration included in the first and second side light spots LBs1 and LBs2 are the same and only the signs are reversed. The amplitude of SPP1 is equal to the amplitude of the second side push-pull signal SPP2 from the second side light spot LBs2, and the polarities of the two signals are opposite to each other. That is, the phase is 180 degrees out of difference. Therefore, the sum of these side push-pull signals is zero.

When there is a radial tilt, the radial tilt causes coma aberration, so the amount of coma aberration at the first and second side light spots Lbs1 and Lbs2 changes. As will be described later, when there is a radial tilt, if the coma aberration of either one of the first and second side light spots LBs1 and LBs2 increases, the other coma aberration is reduced, thereby reducing from one side light spot. The amplitude of the detected side push pull signal is different from the amplitude of the side push pull signal detected from other side light spots, and the polarities of the signals are reversed. Therefore, the sum of the side push pull signals is not zero. Here, even when there is a radial tilt, the relative positions of the first and second side light spots LBS1 and LBS2 do not change with each other.

The third differential actuator 171 uses the defocused _first optical spot LB ₁ formed in the first and second light receiving regions 161 and 163 of the center photodetector 160 to store the optical information storage medium. Generate a first center push-pull signal CPP1 from the center light spot LBm focused on 20. The first center push-pull signal CPP1 is a difference signal between detection signals of the first and second light receiving regions 161 and 163 obtained by dividing and receiving the defocused first light spot LB ₁ .

The fourth differential motor 173 may defocus the second and third light spots LB ₂ and LB ₃ formed in the third and fourth light receiving regions 165 and 167 of the center photodetector 160. To generate a second center push-pull signal CPP2 from the central light spot LBm focused on the optical information storage medium 20. The second center push-pull signal CPP2 is a difference signal of detection signals of the third and fourth light receiving regions 165 and 167 that receive the second and third light spots LB ₂ and LB ₃ , respectively. .

The first and second center push-pull signals CPP1 and CPP2 are sum signals of detection signals of the first to fourth light receiving regions 161, 163, 165, and 167 of the center photodetector 160. Can be normalized by

The fifth differential 175 receives the first and second center push-pull signals CPP1 and CPP2 and outputs a correction signal CS = CPP1-CPP2 which is the difference signal.

The gain adjuster 178 receives the correction signal CS and applies a predetermined gain k corresponding to the correction coefficient.

The sixth motor 177 receives a correction signal applied to the sum signal PP1 + PP2 of the first and second side push-pull signals SPP1 and SPP2 and a predetermined gain k, that is, k × CS. Output the difference signal. The difference signal output from the sixth differential motor 177 becomes a radial tilt signal (RTS) in which an objective lens shift that satisfies Equation 1 described later is corrected.

The signal processor 170 may further include an adder 179 that receives the first and second center push-pull signals CPP1 and CPP2 and outputs the sum signal CPP1 + CPP2. The sum signal CPP1 + CPP2 of the first and second center push-pull signals CPP1 and CPP2 output from the adder 179 corresponds to a conventional push-pull signal and may be used as an input for a tracking servo. .

Here, the first and second side push-pull signals SPP1 and SPP2 or the radial tilt signal RTS corrected by the objective lens shift detected using the first and second side push-pull signals SPP1 and SPP2 are sum signals CPP1 + CPP2 of the center push-pull signal. Can be normalized by

According to the present invention as described above, it is possible to detect a radial tilt signal in which the objective lens shift is corrected. Therefore, even when the objective lens shift occurs, accurate radial tilt detection is possible.

On the other hand, in the optical recording and / or reproducing apparatus according to the present invention described above, the reproducing signal can be obtained as the sum signal of the detection signals of all the light receiving regions of the central photodetector 51 or 160.

The collimating lens 13 may be disposed between the light source 10 and the optical path converter 15. In this case, the optical pickup collects the light reflected from the optical information storage medium 20 toward the photodetector 150, so that a light spot having an appropriate size is formed on the photodetector 150. It is preferable to further provide. The sensing lens 23 may be provided to detect a focus error signal using the astigmatism principle by adjusting the astigmatism of the return beam traveling to the photodetector 150. In FIG. 1, reference numeral 17 is a reflection mirror for vertically bending an optical path.

In the above, specific examples of the optical pickup and optical recording and / or reproducing apparatus capable of realizing the radial tilt signal detection method according to the present invention have been described and illustrated, which are merely illustrative.

That is, the optical configuration of the optical pickup according to the present invention and the configuration of the optical recording and / or reproducing apparatus having the same can be variously modified.

In particular, the structure of the photodetector 150 and the technical configuration of the signal processor of the optical recording / reproducing apparatus according to the present invention may be variously modified. Also, the optical configuration of the optical pickup illustrated in FIG. 1 is merely an example, and the optical configuration of the optical pickup may be variously modified.

5 is a graph illustrating the effect of the objective lens shift on the radial tilt signal. The results of FIG. 5 show that the radial tilt signal (ie, the first and second side push-pull signals without correction of the objective lens shift detected for the objective lens shift under the conditions of W ₃₁ = 1λ, BD, radial tilt angle 0.25 °) Sum signal, hereafter referred to as RTS _correction signal for convenience). As can be seen in Figure 5, the RTS _{pre-correction} signal can be affected by the objective lens shift.

A general trend in the field of information storage, particularly in the field of optical information storage, is to increase the recording density further. An objective lens having a high number of apertures is used for optical pickup to generate a small spot size on the disk-shaped optical information storage medium (ie, optical disk) surface. Normally, the objective lens is moved by the actuator in the radial direction to perform tracking. The relative position of the objective lens relative to the photodetector is not fixed, whereby the light reflected from the optical information storage medium and formed into spots defocused on the photodetector moves across the photodetector in response to the objective lens shift.

As such, when recording / reproducing the optical information storage medium, an objective lens shift may occur, and this objective lens shift may affect the radial tilt signal, as can be seen in FIG. 5. As confirmed by the inventors, an objective lens shift of 0.4 mm in a BD system results in the same as having a radial tilt signal corresponding to a tilt angle of about 6 °.

However, according to the method of detecting the radial tilt signal canceling the influence of the objective lens shift and the optical recording and / or reproducing apparatus which can realize the same, the accurate radial tilt can be detected even in the objective lens shift. .

The _pre- RTS _correction signal is a sum signal of the first side push-pull signal SPP1 and the second side push-pull signal SPP2, that is, RTS _{before correction} = SPP1 + SPP2.

According to the present invention, as a result of subtracting a signal obtained by multiplying a predetermined correction coefficient k by a correction signal CS resulting from the objective lens shift from the RTS _correction signal, the radial tilt signal RTS from which the objective lens shift is corrected is obtained. Obtained ..

Equation 1 shows a radial tilt signal (RTS) in which an objective lens shift obtained according to the radial tilt detection method according to the present invention is corrected.

RTS = SPP1 + SPP2-k × CS

Here, k is a constant optimized for a defined objective lens shift interval, which is a radial tilt signal correction coefficient. In Equation 1, CS is a correction signal and satisfies CS = CPP1-CPP2.

At this time, the radial tilt signal (RTS) characteristic of the objective lens shift detected according to Equation 1 is the same as FIGS. 8 to 12. 8 to 12, which will be described later, show a characteristic of the radial tilt signal (RTS) obtained according to Equation 1 in the absence of an objective lens shift. When there is no objective lens shift, the correction signal CS term can be zero. Even when there is an objective lens shift, since the influence is corrected, a radial tilt signal as shown in FIGS. 8 to 12 can be obtained regardless of whether or not an objective lens shift is present.

Hereinafter, when using the optical recording and / or reproducing apparatus according to an embodiment of the present invention, the first and second side light spots (LBs1) formed on the optical information storage medium 20, depending on whether or not radial tilt The layout change of the LBs2 and the change of the light intensity distribution in the exit pupil will be described, and the characteristics of the detected radial tilt signal will be described. The radial tilt signal described below is detected for a recordable land / groove optical information storage medium, that is, a BD (Blu-ray Disc).

6 and 7 respectively illustrate the first and second side light beams having opposite signs and having a predetermined amount of coma aberration when there is no radial tilt and when there is a radial tilt of 1 °, respectively. Layout when the first and second side light spots LBs1 and LBs2 are formed on the beams) and the light intensity at the exit holes of the first and second side light beams reflected from the optical information storage medium 20. Show the distribution. The exit hole refers to an exit hole in which a light beam reflected from the optical information storage medium 20 passes through the objective lens 21.

Here, the radial tilt of the optical information storage medium 20 causes coma aberration. In the presence of the radial tilt, the amount of coma in the first and second side light spots LBS1 and LBS2 changes. That is, when the radial tilt occurs, the amount of coma in one of the first and second side light spots LBS1 and LBS2 increases, while the amount of coma decreases in the other. As such, when the radial tilt occurs, the shape and size of the first and second side light spots LBS1 and LBS2 are different. At this time, the relative positions of the light spots do not change because the influence of the coma induced by the tilt on all the light spot positions is the same. The influence of coma induced by the tilt is approximately linear, as can be seen in FIG. 11 described below, for the small angular ranges considered.

6 and 7 (a) shows a first side light spot LBs1 having a coma aberration of W ₃₁ = -1 lambda basically formed on the optical information storage medium 20, (b) The light intensity distribution in the exit hole of the first side light beam reflected from the information storage medium 20 is shown. (c) shows the second side light spot LBs2 basically having a coma aberration of W ₃₁ = + 1λ formed on the optical information storage medium 20, and (d) shows the optical information storage medium 20 It shows the light intensity distribution in the exit hole of the second side light beam reflected from.

As can be seen in FIG. 6, when there is no radial tilt, the first and second side light spots LBs1 formed by the first diffractive optical element 11 and formed on the optical information storage medium 20 ( LBs2) have the same amount of coma aberration of opposite signs. When looking at the light intensity distribution in the exit hole of the first and second side light beams, the sum of one light intensity and the sum of the other light intensities become equal to each other, and the difference becomes zero. Accordingly, the radial tilt signal becomes a zero value.

However, when the optical information storage medium 20 is radially tilted by 1 °, as shown in FIG. 7, for example, the amount of coma aberration of the first side light spot LBs1 decreases, whereas the second side light The coma aberration amount of the spot LBs2 increases. And, looking at the light intensity distribution in the exit hole of the first and second side light beams, the light intensity on either side of each light beam is smaller than before, and the light intensity on the other side is larger than before. Therefore, the sum of one light intensity and the other light intensity of the first and second side light beams are different from each other, and the difference does not become zero. Accordingly, the radial tilt signal has a predetermined value.

FIG. 8 illustrates a first side push-pull signal SPP1 and a second side light spot from the first side light spot LBs1 formed on the optical information storage medium 20 when there is no radial tilt as shown in FIG. 6. The second side push-pull signal SPP2 from LBs2 and the radial tilt signal RTS calculated according to Equation 1 above are shown.

FIG. 9 illustrates a first side push-pull signal SPP1 from a first side light spot LBs1 formed on the optical information storage medium 20 and a second side when there is a radial tilt of 1 ° as shown in FIG. 7. The second side push-pull signal SPP2 from the side light spot LBs2 and the radial tilt signal RTS calculated according to Equation 1 above are shown.

As can be seen from FIG. 8, in the absence of a radial tilt, the first and second side push-pull signals SPP1 and SPP2 have substantially the same amplitude and differ only in phase by 180 degrees. The radial tilt signal (RTS) obtained according to Equation 1 above becomes zero.

On the other hand, as can be seen from Figure 9, when there is a radial tilt, the first and second side push-pull signal (SPP1) (SPP2) is the amplitude of each other and the phase is also different, A radial tilt signal (RTS) obtained according to equation 1 is obtained.

The radial tilt signal (RTS) obtained at this time is a typical push-pull signal (PP) for the center light spot (LBm) having no basic coma aberration formed on the optical information storage medium 20, as shown in FIG. In comparison, the amplitude is considerably larger than about half of a typical push-pull signal PP. In FIG. 10, the center push-pull signal PP is shifted by λ / 2 for convenience of comparison. In the push-pull signal PP and the radial tilt signal RTS shown in FIG. Results in comma aberration of W ₃₁ = 1λ of opposite signs. The conventional push pull signal PP substantially corresponds to the sum signal CPP1 + CPP2 of the first and second center push pull signals.

Fig. 11 shows the relationship between the radial tilt detection sensitivity and the coma amount of the side light spots when using the radial tilt detection method according to the present invention. The results in FIG. 11 show the amount of coma W ₃₁ included in the side light spot, with a radial tilt of 0.25 ° relative to BD (numerical aperture (NA) = 0.85, track pitch (TP) = 0.32μm). The radial tilt signal is detected. Referring to FIG. 11, when the comma W ₃₁ becomes larger than 1λ, the radial tilt detection sensitivity no longer increases. Therefore, for radial tilt detection, it is preferable that the side light spot includes a coma W ₃₁ of approximately up to about 1 lambda.

12 shows a radial tilt signal according to the radial tilt angle when using the radial tilt detection method according to the present invention. The amplitude of the radial tilt signal (RTS) shown in FIG. 12 is the amplitude of a typical push-pull signal, i.e., essentially coma-free, when the side light spot contains 1 lambda for BD. Normalized by the amplitude of the center push-pull signal (CPP) obtained from the spot. When the radial tilt angle θ is 0.25 °, 0.5 °, 0.75 °, 1.0 °, the amplitudes of the radial tilt signal RTS are about 0.13, 0.24, 0.37, 0.49.

As can be seen in Figure 12, the amplitude of the radial tilt signal (RTS) detected in accordance with the present invention increases approximately linearly with the radial tilt angle, and changes sensitively to the radial tilt angle. In addition, the radial tilt signal RTS of FIG. 12 is normalized by a conventional push pull signal, and the amplitude of the radial tilt signal RTS is considerably large in comparison with the conventional push pull signal. Therefore, the radial tilt degree can be detected accurately.

According to the radial tilt detection method according to the embodiment of the present invention as described above, the side light spot for tilt detection is irradiated on the optical information storage medium 20 in proximity to the central light spot used for recording / reproducing Therefore, it is possible to obtain information about the local tilt variation in the vicinity of the central light spot. In addition, when applied to a recordable land / groove medium such as a BD, as can be seen from the result of FIG. 12, it is possible to realize a sufficient tilt detection by exhibiting a sufficiently large tilt detection sensitivity.

The radial tilt detection method and the optical recording and / or reproducing apparatus capable of realizing the radial tilt according to the embodiment of the present invention as described above remove the component caused by the objective lens shift, and the radial tilt with the objective lens shift corrected. Since the signal can be detected, it is very useful even when there is an objective lens shift.

 On the other hand, in the optical recording and / or reproducing apparatus according to the present invention described above, the reproducing signal can be obtained as the sum signal of the detection signals of all the light receiving regions of the central photodetector 160.

As described above, the radial tilt detection method and the optical recording and / or reproducing apparatus capable of realizing the same provide high sensitivity tilt detection for a recordable land / groove type (RAM, R, RW type) optical information storage medium. Can be implemented. In addition, at a radial tilt angle of 1 ° for the BD optical pickup, a sufficient amount of radial tilt signal corresponding to 0.5 of the typical push-pull signal amplitude can be guaranteed. In addition, the radial tilt signal obtained by another embodiment of the present invention, which is adapted to correct the influence of the objective lens shift in the radial tilt signal, is not substantially affected by the objective lens shift. As confirmed by the inventors, the radial tilt detection error is less than 0.1 ° in the +/- 0.4mm objective lens shift interval for the BD optical pickup.

According to the present invention as described above, it has an enhanced tilt detection sensitivity capable of accurately detecting the tilt of the recordable land / groove optical information storage medium, and local tilt detection near the center light spot is possible. In addition, accurate radial tilt signal detection is possible even in the objective lens shift.

Claims (10)

Forming a central light spot on the optical information storage medium and first and second side light spots having comma aberrations of opposite signs when the optical information storage medium is not tilted on both sides of the central optical spot in the tangential direction; Steps; Divides a central light beam corresponding to the central light spot reflected from the optical information storage medium in three spatially, and divides the first light region corresponding to one light region in the tangential direction and the remaining light region in two radial directions. Spatially dividing into second and third light areas corresponding to the two light areas; Detecting the first optical spot corresponding to the first optical region by dividing the optical beam into two radial directions, and detecting the second and third optical spots corresponding to the second and third optical regions, respectively; Dividing and detecting the first and second side light beams corresponding to the first and second side light spots reflected from the medium in a radial direction, respectively; The first center push-pull signal is detected as the difference between the signals detected by dividing the first light spot in the radial direction, and the second center push-pull signal is detected as the difference between the signals that detect the second and third light spots. Making a step; Using the first and second side light beam detection signals, a first side push pull signal from a first side light spot formed on the optical information storage medium and a second side push pull signal from a second side light spot Detecting; A radial obtained by obtaining a correction signal as a difference between the first and second center push-pull signals and subtracting the correction signal multiplied by a predetermined coefficient from a sum signal of the first and second side push-pull signals; Detecting a tilt signal; and a method of detecting a radial tilt. The method of claim 1, wherein the first and second side light spots have the same amount of coma aberration of opposite signs when the optical information storage medium is not tilted. The radial of claim 1, wherein the first and second side light spots are formed on an optical information storage medium such that the first and second side push-pull signals detected therefrom have a phase difference of 180 °. Tilt detection method. The method of claim 1, wherein the first and second side light spots are formed on the optical information storage medium symmetrically with respect to a center light spot in a tangential direction. A light source; The light beam emitted from the light source is diffracted, divided into a central light beam and first and second side light beams, and a central light spot corresponding to the central light beam on the optical information storage medium, and optical information storage in both of the central light spots. A first diffractive optical element for forming first and second side light spots corresponding to the first and second side light beams having comma aberrations opposite to each other when the medium is not tilted; An objective lens for focusing incident light and focusing on an optical information storage medium; The light beam reflected from the optical information storage medium is spatially divided into a first light region corresponding to one light region in the tangential direction, and a second light region corresponding to two light regions in which the remaining optical region is divided into two in the radial direction. A second diffractive optical element for spatially dividing into two and third optical regions; Defocused first to third light spots corresponding to the first to third light regions are formed, the first light spot is divided into two in the radial direction, and the second and third light spots are respectively detected. And a photodetector comprising a central photodetector configured to divide the first and second side light beams reflected from the optical information storage medium in a radial direction, respectively, and detecting the first and second side photodetectors. and, A first side push-pull signal from a first side light spot formed on the optical information storage medium and a second side push from a second side light spot using the detection signals of the first and second side photodetectors The first center push-pull signal, the second and third light spots are detected as the difference between the signals detected by detecting the pull signal and dividing the first light spot in the radial direction by using the detection signals of the center photodetector. Detect a second center push-pull signal as a difference between the detected signals, detect a correction signal as a difference between first and second center push-pull signals, apply a predetermined coefficient to the correction signal, and apply the first and second side And a signal processor configured to detect a radial tilt signal in which an objective lens shift is corrected by subtracting a correction signal to which a predetermined coefficient is applied from the sum of the push-pull signals. Coming up. 6. The optical recording and / or reproducing apparatus according to claim 5, wherein the first and second side optical spots have the same amount of coma aberration of opposite signs when the optical information storage medium is not tilted. 6. The optical information storage medium of claim 5, wherein the first and second side light spots are formed on the optical information storage medium such that the first and second side push pull signals detected therefrom have a phase difference of 180 degrees. Optical recording and / or reproducing apparatus. 6. The optical recording and / or reproducing apparatus according to claim 5, wherein the first and second side light spots are formed on the optical information storage medium symmetrically with respect to the center light spot in the tangential direction. According to claim 5, The second diffractive optical element is provided with a polarization diffraction element for diffracting the light selectively in accordance with the polarization of the incident light, And a quarter-wave plate for changing the polarization of the incident light between the second diffractive optical element and the objective lens. 6. The optical diffraction device of claim 5, wherein the second diffractive optical element has first to third diffractive regions for dividing a light beam into the first to third optical regions. And the first and third diffractive areas are formed to correspond to the semicircles of the light beam, and the second and third diffractive areas are formed to correspond to the quadrants of the light beam.

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